It may be that the issue is related to it just ringing to the attendant because DIL is set to 0. (I was using "Hunt Group 0" as short-hand for saying that it was the attendant station, mostly because I was mis-interpreting the way that the DIL worked when it was set to 0). This is the first time that I've had this particular behavior occur, though, and I've worked on a lot of systems with similar DIL settings.

The CO lines are POTS lines.

I can call each individual voice mail port by extension number and it answers correctly.

Delay Ring Timer is currently set to 8; it was originally set to 12 but I dropped it down in order to test if there was some other rolldown behavior kicking in on the CO side (the customer had vague recollections of there previously being something set up on the CO side to forward calls to his cell phone, but it had been a while since it had been set up like that so he wasn't sure one way or the other).

If I connect to the system in night mode and log in to 900 it plays the correct greeting.